Housing

ABSTRACT

The invention relates to a housing for an electric or an electronic component, in particular a motor vehicle control unit, for which the housing parts or housing connections are designed such that the electric or electronic components are sealed watertight and airtight. Such housings, which are composed if only in part of a thermoplastic synthetic material, are provided with a pressure compensation feature. As a result, the pressure inside the housing is constantly adapted to the outside pressure. With this type of pressure adaptation, it is not possible for gases, particularly water vapor, to permeate the synthetic housing under pressure and reach the electric or electronic components. As a result, damage caused by humidity is greatly reduced and the service life is increased.

BACKGROUND OF THE INVENTION

The invention relates to a housing for an electric or electroniccomponent, in particular a motor vehicle control unit, including aone-part or multi-part container and one or more one-part or multi-partsealing devices.

Electric and electronic components, in particular electronic controlunits, as a rule are mounted inside a housing to protect them againstenvironmental influences, such as mechanical effects, dust, andhumidity. If the housing is used in a motor vehicle, these requirementsare particularly high. Housings of this type must protect the sensitiveelectronic components from moisture, which can enter the housing inliquid form as water or in gaseous form as water vapor. As a rule, thehousings are made at least in part of a thermoplastic syntheticmaterial. These synthetic parts are watertight, but not gas-tight, sothat water in a gaseous form can penetrate. If a multi-part housing issealed watertight with corresponding seals, no liquid can penetrate, butgas can reach the inside of the housing. The following applies in thatcase: $Q = {P*\frac{A*t}{d}}$

Q: Amount of gas penetrating in cm³ or amount of water vapor in g

A: Surface in cm²

t: Effective time in days

d: Wall thickness in cm

P: Permeation constant in cm²/t (gas) or g/(cm*t) (water vapor)¹

However, if the pressure outside of the housing differs from thepressure on the inside of the housing, which is generated above all bythe temperature difference between the inside of the housing and theoutside of the housing, air can reach the inside of the housing. Thefollowing applies in that case: $Q = {P*\frac{A*t*\delta \quad p}{d}}$

Q: Amount of gas penetrating in cm³ or amount of water vapor in g

A: Surface in cm²

t: Effective time in days

δp: Difference in pressure in cm mercury column

d: Wall thickness in cm

P: Permeation constant in cm²/t (gas) or g/(cm²*t) (water vapor)

However, the air also contains gaseous water vapor, which penetrates thesynthetic material and enters the housing because of its smallerparticle size and owing to the pressure difference. Given the followingparameters, a non-negligible amount of water can accumulate in thehousing in the motor vehicle region. This is true for a relativehumidity level of 85% on the outside and 0% relative humidity on theinside and a temperature of 20° C. and 1 bar air pressure.

P=2.1 10⁻⁶ g/(cm²t) for polybutylene terephthalate

A=32 cm²

d=1.5 mm

t=15 years=5475 days wherein:

10% operating time (547.5 days) at 20° C. no pressure difference 20%operating time (1095 days) at 40° C. δp = 0.068 bar = 5.17 cm 50%operating time (2737.5 days) at 60° C. δp = 0.137 bar = 10.41 cm 20%operating time (1095 days) at 80° C. δp = 0.2 bar = 15.2 cm Q_(total) =Q_(20° C.) + Q_(40° C.) ++ Q_(60° C.) + Q_(60° C.) = 0.25 g + 2.5 g +12.8 g + 7.5 g = 23 g

It means that over the total service life of a motor vehicle, in theworst case 23 g water enter through a synthetic housing part with asurface of 32 cm² and a thickness of 1.5 mm. The condensed water can doconsiderable damage to the electronic components. For example, itchanges the conductivity between the various components, which can leadto short-circuits and causes oxidation, meaning rusting, of contacts.For those reasons, housings were provided until now with so-calledpressure-equalizing openings, where a pressure compensation can occurbetween the housing inside and the environment. To prevent water fromentering at the openings in the housing, these were closed off with awatertight and breathable foil, e.g. as known under the name Goretex orSympatex, so that the electronic circuit is protected against waterdamage and moisture damage. This state of the technology is reflected inthe German Patent Application No. 197 08 116.9.

It is disadvantageous in this case that an additional operational stepis required for closing off the pressure-compensation openings with thewatertight and breathable foil. Such watertight and breathable foils arevery expensive. Furthermore, it is a disadvantage of such foils thatthey reduce the diffusion rate as a result of the pressure compensation,to be sure, but are also water vapor permeable.

SUMMARY OF THE INVENTION

Thus, it is the object of the invention to create a housing of theaforementioned type, which does not have the previously listeddisadvantages and which protects an electronic or electric componentreliably against environmental influences.

This object is solved according to the invention. Closing off thecontainer to be watertight with a movable sealing device inside or onthe container to change the inside volume by permitting movement betweenthe container and the sealing device or by having the container or thesealing device be fully or partially expendable. The basic idea behindthe invention is that the inside volume of the housing is variable,depending on the pressure conditions, thus resulting in pressurecompensation. Less moisture reaches the inside of the housing as aresult of this pressure adaptation, which is achieved through anincrease or decrease of the housing inside volume. Owing to thispressure adaptation, less water vapor can permeate the syntheticmaterial and reach the inside of the housing. The changeable housinginside volume can be realized in two different ways. One option providesfor a mutual displacement of the housing parts. The other optionprovides that at least a portion of the housing is expandable.

The advantages achieved with the invention are that no liquid and no gasenter this housing as a result of pressure differences. The electric andelectronic components are protected reliably inside the housing againstdamaging environmental influences. At the same time, the life expectancyof components in such housings is increased strongly. Based on theprevious calculations, only 2.5 g instead of 23 g of water would thenenter the housing.

Advantageous modifications of the invention are possible. For example, aso-called pressure compensation element may be provided on one housingpart. This pressure compensation element is movable and changes its sizeand thus the inside volume of the housing in dependence on the pressureconditions. Another advantageous modification of the invention consistsin that an adhesive connection or a seal is elastic, as a result ofwhich the housing parts can be mutually displaced and the housing volumecan thus be changed. The same effect, namely a variable housing insidevolume, is achieved in that a plug, which closes off the housing, isattached movably in a plug-in device in the housing, so that it can bemoved back and forth.

Several exemplary embodiments of the invention are to be illustratedwith the aid of FIGS. 1 to 5.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a side view of a housing with pressure compensation element;

FIG. 1b is a sectional view of a pressure compensation element;

FIG. 2 is a sectional view of a housing with movable insulating ring;

FIG. 3 is a sectional view of a housing with movable insulating sealinglip;

FIG. 4a is a sectional view of a housing with elastic adhesive orsealing material;

FIG. 4b is a simplified sectional view of a housing with elasticadhesive or sealing material;

FIG. 5a is a sectional view of a housing with deformable housing part,having identical inside pressure and outside pressure;

FIG. 5b is a sectional view of a housing with deformable housing partand negative pressure inside the housing;

FIG. 5c is a sectional view of a housing with deformable housing partand excess pressure inside the housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a shows a view from the side of a housing 6 with pressurecompensation element 3. On the one hand, the housing 6 consists of athermoplastic synthetic container 2, e.g. made of polybutyleneterephthalate (PBT). This synthetic material is impermeable to liquids,especially water, but can be penetrated by gaseous materials. Thesolution diffusion progresses in three stages. First, the diffusingmaterial is absorbed at the side surface with the higher materialconcentration. Subsequently, the material to be absorbed moves withinthe synthetic material from the side with the higher concentration inthe direction of the side with the lower concentration. Finally, thematerial absorbed by the synthetic material is deposited on the sidewith the lower material concentration. The solution diffusion depends onthe pressure conditions between inside wall and outside wall, aspreviously described.

Furthermore, this housing 6 comprises a bottom 1 that closes off thesynthetic container 2 on the bottom. This bottom 1 can be made of metalor a synthetic material. The container 2 also comprises a plug-in device4 that is open in the contact region, said location being closed offwith the aid of a plug 5. A pressure compensation element 3 isfurthermore mounted on the container, the size and form of which canchange in dependence on the prevailing pressure differences. Thepressure compensation element 3 is designed to resemble an accordian, asshown in the detailed view of the pressure compensation element 3 inFIG. 1a. Said pressure compensation element 3 consists of a rubber-typematerial 8 and closes off an opening 9 in the container 2 with the aidof a closing part 10. The pressure compensation element 3 furthermoreprojects toward the inside of the container 2 where it requires more orless space, depending on its inherent volume 7. The inherent volume 7depends on the pressure conditions because the shape changes due toforces acting upon it as a result of the accordian like structure, thatis by expanding or contracting. With such a pressure compensationelement, it does not matter whether it projects toward the inside of thehousing or away from the housing outside and on which part of thehousing it is mounted. It is only important that it changes the insidevolume of the housing by changing its own shape. The shape of thepressure compensation element really is not important. The pressurecompensation element can also be embodied as a balloon that changes itsshape depending on the pressure.

FIG. 2 illustrates another exemplary embodiment. Shown is a sectionthrough the housing, which has a movable insulating ring 12 in theplug-in region 4. The housing for this embodiment also consists of acontainer 2 with a plug-in device 4. The electronic components to beprotected are inside the container, on a circuit board 11. Theseelectronic components are connected via contact pins 14 with the plug 5.The container is closed off from below with a bottom 1 and is scaledwith a plug 5, which seals the container 2 in the plug-in device 4. Thesealing ring 12 makes it possible for the plug 5 to be moved back andforth inside the plug-in device 4 and, at the same time, provide awater-tight or gas-tight seal for the housing, depending on thematerial. The sealing ring 12 can be mounted fixedly in the plug-indevice 4 as well on at the plug 5 or can be positioned movably in aguide 13, as illustrated. It is only important for this exemplaryembodiment that the plug 5 or another seal is movable inside the plug-indevice 4 or another sealing device, without loss of the sealing effecttoward the outside. It is furthermore important that the housing insidevolume is changeable by moving the plug 5 back and forth and that thisback and forth movement is controlled by the pressure difference, sothat a pressure compensation between the housing inside and theenvironment can occur. The exemplary embodiment shown in FIG. 3 is alsobased on this principle, wherein a movable sealing lip 15 ensures thatthe plug 5 is movable inside the plug-in device 4. It makes sense ifthis sealing lip is attached to the plug-in device or the plug. The lipfurthermore is wide enough and elastic enough so that it fits flushagainst the inside wall of the plug-in device during a plug movement,thereby reliably sealing the housing at that location. Rubber-typematerials are preferred for the sealing lip and the sealing ring.Another embodiment, which permits compensating the pressure by adaptingthe inside volume of the housing, is shown in FIGS. 4a and 4 b. FIG. 4aalso shows the housing, for which the container holds the electroniccomponents to be protected and is closed off by a bottom plate 1 and theplug 5. In this case, the device effecting the adaptation of the volumeinside the housing to the existing pressure conditions consists of anelastic adhesive or an elastic sealing mass 16 between bottom 1 andcontainer 2. This adhesive or this sealing mass is expandable and toughand adheres to the bottom 1 and the container 2, even if force isapplied, so that the movable sealing device is also reliablyimpenetrable. These facts are also illustrated in FIG. 4. An up and downmovement of the bottom 1, a lid or any other closing device or thecontainer 2 is possible in the direction of the arrow as a result of theelastic adhesive or the elastic sealing mass 16. In the process, theinside volume changes until the pressure is compensated.

The exemplary embodiments shown in FIGS. 5a, 5 b and 5 c illustrateanother option for achieving a pressure compensation through volumeadaptation inside the housing. The housing shown therein has at leastone housing part or a seal that is expandable. FIG. 5a illustrates thebalanced state where the temperature and the pressure inside the housingare the same as the environmental conditions outside of the housing 6and there is no force acting upon the lid 1. If the temperature dropsinside the housing or if the temperature rises outside of the housing,then a low pressure develops, the expandable housing part 1 is deformedtoward the inside and reduces the inside volume until the pressure isequalized once more. On the other hand, if the temperature rises insidethe housing or the temperature drops outside of the housing, then anexcess pressure develops and the expandable housing part 1 is deformedtoward the outside, that is until the volume is high enough for theinside pressure and the outside pressure of the housing 6 to remainconstant.

What is claimed is:
 1. A housing having a single variable inside volumefor an electric or electronic component, comprising: a one-part ormulti-part container; at least one one-part sealing device; and sealingmeans for closing off the container in a watertight manner, wherein thecontainer, the sealing means and the at least one sealing devicetogether define the single variable inside volume and wherein at leastone of the container and the at least one sealing device is expandableto change the single variable inside volume of the housing.
 2. A housingaccording to claim 1, wherein at least one of the container and the atleast one sealing device has an expandable pressure compensation elementwhich increases or reduces the single variable inside volume of thehousing depending on the pressure difference between an area inside thehousing and an area surrounding the housing.
 3. A housing according toclaim 1, wherein the component is a motor vehicle control unit.
 4. Ahousing having a single variable inside volume for an electric orelectronic component, comprising: a one-part container; at least oneone-part or multi-part sealing device; and sealing means for closing offthe container in a watertight manner; wherein the container, the sealingmeans and the at least one sealing device together define the singlevariable inside volume and the at least one sealing device is movablerelative to the container to change the single variable inside volume ofthe housing, via a back and forth movement between the container and theat least one sealing device.
 5. A housing according to claim 1, whereinthe component is a motor vehicle control unit.
 6. A housing according toclaim 1, wherein at least one movable connection between the containerand the at least one sealing device is provided by an elastic adhesiveor an elastic sealing mass, to permit relative movement between the atleast one sealing device and the container to change the single variableinside volume of the housing.
 7. A housing according to claim 6, whereinthe at least one sealing device comprises a plug which can be moved backand forth inside a plug-in device.